The present invention is related to the field of treating samples on microscope slides and more specifically to the field of heat induced antigen recovery and staining.
Antigen recovery, also known as antigen unmasking, antigen epitope unmasking, antigen retrieval or heat induced epitope recovery (HIER) is a process in which biological samples (e.g., cells, tissues, blood, fluids) are treated under heat with a series of aqueous or non-aqueous reagents and buffers (e.g., citrate, EDTA, and urea) for the purpose of exposing the presence of specific types of antigens or biochemical features in the biological samples. HIER is regarded as a pre-treatment procedure to be performed prior to the beginning of a specific staining protocol to identify cellular components.
Biological samples must be preserved after removal from the body. This preservation process, known as fixation, kills and localizes the biological material. One of the most common fixatives used widely in the preservation of biological materials is formalin, a 10% aqueous solution of formaldehyde. This fixative, along with other widely utilized fixatives, produces a cross-linking network around specific sites in the biological material. These sites are known as antigens, and during the fixation process become “masked,” by the fixative and thus “invisible” to detection by certain stains. HIER is used as a pre-treatment process to “unmask,” “retrieve” or “recover.” This process is usually conducted on formalin fixed paraffin embedded tissue sections or cellular preparations mounted on microscope slides.
U.S. Pat. No. 5,244,787 teaches a process of antigen retrieval wherein one or more slides are placed in an aqueous solution within a microwave oven and heated to boiling or near-boiling temperatures. These slides are all treated together in a rack that has been placed in a bath of the solution. The slides are near boiling temperatures for 5-30 minutes, generally around 10 minutes. Due to excessive evaporation from the bath, the patent teaches that the solution should not drop below the biological sample on the slide because drying out of the sample is deleterious. This process further teaches that after boiling or near-boiling for several minutes, usually 5 minutes, one may have to add more solution to the container to prevent the solution from excessive evaporation and subsequent exposure of the samples on the slides. After the addition of more liquid, the process is continued until the desired time is completed. The disclosure of U.S. Pat. No. 5,244,787 is limited to the use of a microwave oven as the source of heating. More recent advances, which have been published, include the use of different types of heating devices such as electric pressure cookers, electric steamers, electric conduction heating surfaces utilizing pressure cookers, steamers, and also steam driving autoclaves (J. of Pathology, 179:347-352, 1996; Biotechnic & Histochemistry, 71(5):263-270, 1996; Biotechnic & Histochemistry, 71(4):190-195, 1996; J. of Histochemistry & Cytochemistry, 45(3): 327-342, 1997).
Although these published methodologies treat the biological sample with different types of solutions and with varying types of chemicals and at different pH's, all teach that all slides are treated together in a bath of the heated solution. After the slides have cooled for a period of time, they are removed from the heating device and they are transferred to another apparatus where they are manually or automatically stained using various reagents. This pre-treatment process of heating and removing the slides from the heating device for staining in a separated apparatus is highly cumbersome and inefficient. The only automated HIER or antigen retrieval instrument available is the BIOGENEX i1000. This instrument, however, still employs the use of the known technology of treating the slides as a group in a container filled with heated solutions. A technician must still remove the slides from the antigen retrieval (heating) instrument and place them in an automated stainer instrument to complete the required staining protocol.
As noted herein, no currently available automated or semi-automated staining instruments specifically teach the ability to heat an aqueous or non-aqueous liquid for the unmasking of antigens. The instruments that do automated or semi-automated staining limit their scope to that task alone, and don't address the task of HIER or antigen retrieval pre-treatments. U.S. Pat. Nos. 5,073,504 and 4,847,208 teach use of a chamber for enclosing and staining a microscope slide but neither teaches use of a heating device to boil a liquid and the user must add the primary antibody manually through a hinged door on top of the chamber. U.S. Pat. Nos. 4,777,020; 4,798,706; and 4,801,431 teach use of a vertical staining “capillary gap” methodology wherein two special slides placed front to front causing an air gap through which liquids are drawn by capillary movement. This gap can only hold a small volume (approx. 300 microliters) of liquid. If heated to near boiling conditions the liquid would evaporate through all four open sides, immediately causing the biological sample to dry. This end result is true also for another capillary gap instrument, shown in U.S. Pat. No. 5,804,141. U.S. Pat. Nos. 5,595,707; 5,654,200; 5,654,199, 5,595,707; and 5,650,327 teach reducing evaporative loss by utilizing an oil layer on top of the aqueous layer. This is somewhat effective in reducing the amount of evaporative loss at 37° C. but the volume of the aqueous layer (approx. 300 microliters) is again minimal, and if heated to boiling, would cause the aqueous layer to dry out leaving only the oil layer present thus damaging the biological sample unless more aqueous reagent was applied during the treatment process. U.S. Pat. No. 5,425,918 also teaches use of small amounts of liquids that are sprayed on the slide and can only heat the slide to 37□C. U.S. Pat. Nos. 5,645,144 and 5,947,167 teach use of an open top chamber present around the slide and use a rotating cover above the slides to reduce evaporation. There is no teaching of high temperature heating of a liquid for a substantial amount of time. Further, even if one would increase the temperature of the slide, the loosely rotating top of the chamber would allow so much evaporative loss that the solution would never reach boiling or near boiling temperatures, nor would it maintain the boiling conditions for 10 minutes or longer. U.S. Pat. No. 5,645,114 teaches use of small volumes of liquids (up to 500 microliters) and has no ability to stop evaporative loss if the slide temperature reaches boiling conditions.
As a result, none of these systems could hold sufficient liquid on top of a slide (e.g., 4 ml) and are enclosed in a chamber which is properly vented to minimize the energy loss from evaporation to cause sufficient heating to boil the liquid on the slide for the length of time generally required to cause antigen unmasking (e.g., 10-30 minutes).
There remains a need for an apparatus which can perform the task of HIER with subsequent staining treatment without the need of switching the slides from one apparatus to another and wherein the treatment of all microscope slides can occur simultaneously thereby increasing efficiency. Of the automated stainers available today, there is not one instrument that has the ability to overcome the inherent problems of heating an aqueous or non-aqueous solution at a sufficient volume without the undesirable effect of evaporative heat loss and subsequent volume decrease of the solution. The negative effects of evaporation are significant. The ability of a liquid to reach boiling or near boiling temperature on a microscope slide is dependent on the containment and control of the steam or vapor generated during the heating process. It is the object of the invention contemplated herein to provide a completely automated HIER apparatus which can recover antigens with multiple types of recovery buffers simultaneously, each specific to its respective microscope slide and which can also be used to stain the microscope slides as well.